Sensitivity of Frequency Dependence of Lung Compliance in Detecting Uneven Time Constants

We have evaluated the sensitivity of frequency dependence (spon-1.5 Hz) of dynamic compliance (Cdyn) and pulmonary resistance (RL) by introducing two bronchial catheters in dog´s lungs. We measured the differential bronchial pressure (Pbr) and defined the transfer ratio (H) as Pbr/Ppleural at points of zero mouth flow. Calculations predict H to be more sensitive compared to Cdyn or RL. We infused 0.5 and 2.0 ¿g/(kg-min) histsnine to cause small airways constriction. With the larger dose, Cdyn, RL, and H all became frequency dependent with no change in RL(spon). With the smaller dose, H(spon) changed throughout the infusion , pnd, had different values from control at 30, 60, and 90breaths/min. However, Hwas frequency dependent in control suggesting that it is sensitive to interlobal anatomical differences. We conclude that the frequency Dependence of Cdyn is the most specific test for detecting small airways constriction.